John M. Hollerbach

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Unrestrained human arm trajectories between point targets have been investigated using a three-dimensional tracking apparatus, the Selspot system. Movements were executed between different points in a vertical plane under varying conditions of speed and hand-held load. In contrast to past results which emphasized the straightness of hand paths, movement(More)
Movement of multiple segment limbs requires generation of appropriate joint torques which include terms arising from dynamic interactions among the moving segments as well as from such external forces as gravity. The interaction torques, arising from inertial, centripetal, and Coriolis forces, are not present for single joint movements. The significance of(More)
The objective of this study was to determine the extent to which subjects modulate their elbow joint mechanical properties during ongoing arm movement. Small pseudo-random force disturbances were applied to the wrist with an airjet actuator while subjects executed large (1 rad) elbow joint movements. Using a lumped parameter model of the muscle, tendom and(More)
An efficent laganglan formulation of manipulator dynamics has been developed. The efficiency derives from recurrence relatons for the veloces, acelan, d generalized forces. The number of addo and multiplicatins varies linearly with the number of joint, as opposed to past laorngan dynamics formulations with an n4 dependence. Wih this formulatbo It should be(More)
The major approaches toward kinematic calibration are unified by considering an end-point measurement system as forming a joint and closing the kinematic loop. A calibration index is introduced, based on the mobility equation, that considers sensed and unsensed joints and single and multiple loops and expresses the surplus of measurements over degrees of(More)
Handwriting production is viewed as a constrained modulation of an underlying oscillatory process. Coupled oscillations in horizontal and vertical directions produce letter forms, and when superimposed on a rightward constant velocity horizontal sweep result in spatially separated letters. Modulation of the vertical oscillation is responsible for control of(More)
Experiments were conducted on length resolution for objects held between the thumb and fore-finger. The just noticeable difference in length measured in discrimination experiments is roughly 1 mm for reference lengths of 10 to 20 mm. It increases monotonically with reference length but violates Weber's law. Also, it decreases when the subject is permitted(More)